The present invention relates to a compressed air motor comprising a piston and a housing, the piston being received in the housing and dividing the housing into two primary chambers of variable volume.
Compressed air motors are frequently used to drive alternating movement pumps. Such pumps are in particular used to pumps viscous products, such as putty, or liquid products, such as paint. Document FR 2,695,965 A1 describes one such pump comprising a compressed air motor.
Compressed air motors generally comprise a housing containing a piston. The piston divides the housing into two chambers, commonly called “upper chamber” and “lower chamber”, which are alternately supplied with compressed air. The alternating injection of compressed air into each of the chambers generates the alternating movement of the piston.
Compressed air motors are frequently equipped with a distributor, which alternately supplies the upper chamber and the lower chamber. The distributor is generally controlled by external control members, of the switch type. Such motors are very reliable, but expensive. Furthermore, the use of distribution and external control members makes the assembly and maintenance of an installation comprising such a motor more complex.
Other types of motors are equipped with an integrated inverter block including a rotary spring. These motors have a simple design, but have reliability problems.
Other types of compressed air motors do not require an inverter or distributors. A compressed air motor is for example known from document FR 484,199 A comprising two distributors supplying the upper and lower chambers supported by a same stem. The stem is moved by the piston between two positions to control the supply of the chambers.
Document DE 19 92 789 U describes a compressed air motor in which two seals supported by a stem control the supply of the upper and lower chambers.
Several examples of compressed air motors in which the supply of the upper and lower chambers is controlled by two valves mounted on a same stem are known from document EP 0,414,268 A1, DE 28 16 617 A1, DE 28 23 667 A1 and EP 0,319,341 A2.
Another type of compressed air motor in which the alternating supply of the chambers is obtained by the movement of a stem is described in document WO 2003/058072 A2.
However, these known compressed air motors often have reliability problems, since in a case where the control stem is stopped in an intermediate position, the two chambers could be supplied at the same time and the motor would then remain blocked. Mechanisms making it possible to keep the stem in its extreme positions exist, but make the structure of the motor more complex.
Other mechanisms for controlling the supply of the upper and lower chambers of a motor cylinder are known. For example, a valve actuator in which a moving sleeve commands the supply of the upper and lower chambers of a cylinder is known from document U.S. Pat. No. 4,974,495 A.